Sulfur absorbents

ABSTRACT

Provided is an improved process for removing sulfur compounds from sulfur contaminated fluid streams by contacting such fluid streams with an absorbent composition comprising zinc oxide, silica, and molybdenum disulfide. The absorbent composition comprising zinc oxide, silica, and molybdenum disulfide is a novel composition which has the desirable properties of high sulfur loading capacity and the ability to be contacted with the hydrogen sulfide containing fluid stream for the removal of such hydrogen sulfide from said fluid stream with a minimum amount of sulfur dioxide slippage. An additional embodiment of the disclosed invention includes a method for minimizing the amount of extrusion die wear during the production of the zinc oxide based absorbent compositions. Extrusion die wear is reduced by adding a quantity of molybdenum disulfide to the zinc oxide absorbent in an amount which provides desirable lubricating properties such that extrusion die wear is reduced during the manufacture of the composition.

This application is a divisional of application Ser. No. 07/718,054,filed Jun. 20, 1991.

This invention relates to sulfur absorbent compositions, the manufactureof sulfur absorbents and their use.

BACKGROUND OF THE INVENTION

The removal of sulfur from fluid streams can be desirable or necessaryfor a variety of reasons. If the fluid stream is to be released as awaste stream, removal of sulfur from the fluid stream can be necessaryto meet the sulfur emission requirements set by various air pollutioncontrol authorities. Such requirements are generally in the range offrom about 10 ppm to 500 ppm of sulfur in the fluid stream. If the fluidstream is to be burned as a fuel, removal of sulfur from the fluidstream can be necessary to prevent environmental pollution. If the fluidstream is to be processed, removal of the sulfur is often necessary toprevent the poisoning of sulfur sensitive catalysts or to satisfy otherprocess requirements.

Various absorption compositions have been used to remove sulfur fromfluid streams when the sulfur is present as hydrogen sulfide. Theseabsorption compositions can be, manufactured by a variety of methodswhich include extrusion production techniques. A problem that is oftenencountered in the production of these absorption compositions isequipment wear caused by the abrasive nature of the absorption materialsbeing manufactured. In certain attempts to produce commercial quantitiesof absorbent compositions, excessive equipment wear and downtime causedby the abrasive characteristics of the absorption material componentshave, in effect, rendered the production of such compositionscommercially unviable.

A further property of which it is desirable for absorption compositionsto have is the ability to absorb large quantities of sulfur. Thiscapability to absorb large amounts or concentrations of sulfur issometimes referred to as "sulfur loading" and is generally reported interms of percent sulfur loading. The term it percent sulfur loading" isgenerally defined as the parts by weight of sulfur absorbed upon thesurface or within the pores of an absorption composition per parts byweight of the total absorbent composition multiplied by a factor of 100.It is desirable to have an absorption composition with the largestpossible sulfur loading capacity.

An additional property desirable for an absorption composition is theability to be regenerable to the original absorbing composition stateafter the absorbing composition bas become spent. An absorbingcomposition generally becomes spent when its sulfur loading capacity hasessentially been used up. It is desirable for the absorbing compositionto be able to undergo numerous regeneration cycles without losing itssulfur loading capacity and other desirable properties.

Even though many absorbing compositions can effectively absorb hydrogensulfide from fluid streams containing hydrogen sulfide, it is notuncommon for many of these absorbing compositions to effectively oxidizesignificant amounts of hydrogen sulfide to sulfur dioxide when contactedwith such fluid streams. The resulting sulfur dioxide is not removedfrom the fluid stream by the absorbent composition and thus passesthrough the absorbent material with the contacted fluid stream. Thisphenomena is sometimes called "sulfur slippage." It is desirable to havean absorption material which bas a high capacity to absorb sulfur from afluid stream and which minimizes the amount of sulfur slippage.

In some absorption compositions, the addition of a promoter compound canbe used to allow for easier regeneration of the absorbing material.

SUMMARY OF THE INVENTION

It is, thus, an object of the present invention to provide an improvedabsorption composition having the desirable properties of high sulfurabsorption capacity, the ability to be repeatedly regenerated and thatis capable of easy regeneration.

It is yet another object of the present invention to provide a method ofreducing equipment wear caused by the abrasive nature of absorbentcomponents and the production of such absorbents.

A still further object of this invention is to provide an improvedprocess for removing sulfur from hydrogen sulfide containing fluidstreams whereby sulfur slippage is minimized.

Yet another object of the present invention is to provide an improvedmethod for removing sulfur compounds from fluid streams containingcontaminating quantities of said sulfur compounds.

In accordance with this invention, there is provided an absorbentcomposition having lubricating properties which comprises a mixture ofzinc oxide, silica, and up to about 25 parts by weight molybdenumdisulfide per 100 parts by weight of the sum weight of the zinc oxide,silica, And molybdenum disulfide. This novel composition bas many of thedesirable physical properties for absorption compositions. Suchproperties include, for example, having a high sulfur loading capacityand having the ability to be easily regenerated with repeatedregenerations without a significant loss in its initial properties.

In another aspect of this invention, there is provided a method ofreducing sulfur slippage in an absorption process for removal ofhydrogen sulfide from a fluid stream having a contaminatingconcentration of hydrogen sulfide which comprises the steps of addingmolybdenum disulfide to a contact material comprising zinc oxide andsilica to thereby produce an absorbent material suitable for use in saidabsorption process. The method further comprises the step of contactingthe fluid stream with the absorbent composition under conditions thatare suitable for removing at least a portion of the contaminatingconcentration of hydrogen sulfide in the fluid stream. In anotherembodiment of the method of reducing sulfur slippage, a sulfurcontaminated fluid stream is contacted with a contact materialcomprising a mixture of zinc oxide, silica, and molybdenum disulfide,which bas been previously calcined, to produce an efficient streamhaving a reduced concentration of the contaminating sulfur compounds.

In accordance with yet another aspect of this invention, there isprovided a method of reducing equipment wear during the production of azinc oxide based absorbent. This method comprises the steps of mixingmolybdenum disulfide with zinc oxide and silica to form a mixture havingcertain desirable lubricating properties followed by adding to themixture a suitable dilute acid to produce an extrudable paste. Theextrudable paste is extruded through an extrusion die to produce anextrudate of the zinc oxide based absorbent.

In a still further aspect of this invention, there is provided a methodof preparing a novel absorbent composition, which has the improvedability to minimize sulfur slippage in q process for absorbing hydrogensulfide from a fluid stream when contacted with said fluid stream in thepresence of a small amount of hydrogen. The method comprises mixing zincoxide, silica, and up to about 25 parts by weight of molybdenumdisulfide per 100 parts by weight of the sum weight of the zinc oxidesilica and molybdenum disulfide to form a mixture. Following the mixingstep, a suitable dilute acid is added to the mixture to form anextrudable paste followed by extruding the extrudable paste andcalcination of the resultant extrudate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, aspects and features of the present invention will beevident from the following detailed description of the invention, theclaims and the drawings in which:

FIG. 1A-1C are a series of graphical representations of process andphysical property data of a comparative absorbent composition and theuse thereof.

FIG. 2A-2C are series of graphical representations of process andphysical property data of the novel absorbent composition and the usethereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with one aspect of the present invention, there isprovided a composition comprising zinc oxide, silica, and up to about 25parts by weight molybdenum disulfide per 100 parts by weight of the sumweight of zinc oxide, silica, and molybdenum disulfide. The compositiondescribed herein has many of the desirable physical properties forabsorption compositions. When utilized in a sulfur removal process, thecomposition bas superior sulfur loading properties and when contactedwith the fluid stream containing sulfur compounds, much of the sulfur isabsorbed by the composition with a minimum amount of sulfur slippage.Furthermore, by utilizing the compound molybdenum disulfide within theabsorption composition, a dual benefit is provided whereby themolybdenum disulfide serves as both a promoter compound for improvingthe regenerability of the absorption composition and a lubricant whichminimizes or reduces the amount of equipment wear when the absorbentcomposition is agglomerated.

One method of producing the absorbent composition is by mixing the zincoxide, silica, and molybdenum disulfide to form a homogeneous mixture.Any suitable method for mixing the component can be used to provide thehomogeneous mixture. Such suitable types of solids-mixing machines caninclude, but are not limited to, tumblers, stationary shells or troughs,muller mixers, which are either batch type or continuous type, impactmixers, and the like. The mixing of the solid particles components canbe conducted during any suitable time period necessary to properlyhomogenize the mixture. Generally, however, the blending time is usuallyless than 60 minutes. Preferably, the mixing time will be in the rangeof from about 2 minutes to about 30 minutes.

Following the mixing of the absorbent components, a dilute acid is addedwith continued mixing in either a batch-wise fashion or continuousfashion to form an extrudable paste. Suitable types of batch mixersinclude, but are not limited to, change-can mixers, stationary-tankmixers, double-arm kneading mixers having any suitable type of agitatorblades such as sigma blades, dispersion blades, multiwiping overlapblades, single curve blades, double-naben blades, and the like. Suitabletypes of continuous mixers can include, but are not limited to, singleor double screw extruders, trough-and-screw mixers and pug mills. Toachieve the desired dispersion of the absorption composition components,the materials are mixed until a homogenous mixture is formed. The mixingtime should be sufficient to give a uniform mixture and, generally, willbe less than about 45 minutes. Preferably, the mixing time will be inthe range of from about 2 minutes to about 15 minutes. The extrudablepaste can then optionally be extruded, dried, and calcined to produce acomposition having the desired properties of a high sulfur loadingcapacity and regenerability.

The absorption composition comprises any suitable mixture of silica,zinc oxide, and molybdenum disulfide which will achieve the desiredabsorbent properties; however, the best ratio of the components dependsupon the optimization of the various physical properties desired and theeconomics of the given use. Generally, because of the large porousvolume and great surface area of silica, it is desirable to use acertain quantity of silica in the absorption composition to impart thedesirable properties of high porosity and high surface area, whichaccommodate the absorption of sulfur compounds. The silica isessentially inert, but when it is incorporated with the zinc oxide andmolybdenum disulfide of the composition, the absorption process isfacilitated. As for the incorporation of the zinc oxide component of thecomposition, because the zinc oxide is the active component, it ispreferred to maximize the amount of this component used in thecomposition within the various constraints mentioned within thisspecification. Furthermore, it has been found that the presence ofmolybdenum in the absorption composition improves the regenerability ofthe absorbent composition and, when molybdenum disulfide is present in amixture of the components during production, equipment wear ismaterially and substantially reduced due to the lubricatingcharacteristics of molybdenum disulfide. Consequently, the use ofmolybdenum disulfide in the absorbent composition, both during theproduction of the absorbent composition and during the use of theabsorbent composition, serves a dual function. It is, therefore,advantageous to use a suitable amount of molybdenum disulfide which bothimparts certain desirable lubricating properties to the absorptioncomponents during manufacture of the absorbent composition and whichimparts the desirable properties for enhancing absorption compositionregeneration.

Any suitable concentration of zinc oxide can be used in the absorptioncomposition which will impart the desirable absorbent properties;however, generally, the zinc oxide will be present in the absorptioncomposition in an amount in the range of from about 10 weight percent toabout 90 weight percent. Preferably, zinc oxide can be present in therange of from about 25 weight percent to about 80 weight percent. Mostpreferably, zinc oxide can be present in the absorption composition inthe range of from about 45 weight percent to about 70 weight percent. Asused herein, the term it weight percent," when referring to componentsof the absorption composition, is defined as parts by weight of thegiven component per 100 parts by weight of the total combined weight ofthe absorption composition multiplied by the factor 100.

The zinc oxide used in the preparation of the absorbing composition caneither be in the form of zinc oxide, or in the form of one or more zinccompounds that are convertible to zinc oxide under the conditions ofabsorption composition preparation described herein. Examples of suchzinc compounds include zinc sulfide, zinc sulfate, zinc hydroxide, zinccarbonate, zinc acetate, and zinc nitrate. Preferably, the zinc oxide isin the form of powdered zinc oxide.

Any amount of silica suitable for imparting the desired porosity can bepresent in the absorption composition and, generally, can be present inthe absorbing composition in an amount in the range of from effectivequantities up to about 90 weight percent. Preferably, silica can bepresent in the range of from about 30 weight percent to about 90 weightpercent. Most preferably, silica can be present in the absorptioncomposition in the range of from about 35 weight percent to about 65weight percent.

The silica used in the preparation of the absorbing composition can beeither in the form of silica, or in the form of one or more siliconcompounds that are convertible to silica under the conditions ofabsorption composition preparation described herein. Any type of silicasuitable for imparting the desired porosity can be used in the absorbingcomposition employed in the process of the present invention. Examplesof suitable types of silica include diatomite, silica, colloid,flame-hydrolyzed silica, hydrolyzed silica, and precipitated silica,with diatomite being presently preferred. Examples of silicon compoundsthat are convertible to silica under the production conditions used inthe preparation of the absorption composition described herein includesilicic acid, sodium silicate, and ammonium silicate.

Any suitable amount of molybdenum disulfide or molybdenite, which willimpart the desired lubricating properties and enhance the ease ofregeneration, can be utilized in the absorbent composition. Themolybdenite utilized in this invention is generally a naturallyoccurring compound but it can also be a synthetically produced compound.Generally, it is preferred that the molybdenite or molybdenum disulfidebe present in the absorbent composition in an amount up to about 25parts by weight molybdenum disulfide or, in the alternative, from atleast a portion to about 25 parts by weight molybdenum disulfide, per100 parts by weight of the sum weight of the zinc oxide, silica, andmolybdenum disulfide. Preferably, however, the molybdenum disulfideshould be present in a concentration in the range of from about 1. partby weight to about 15 parts by weight per 100 parts by weight of thetotal absorption composition. Most preferably, the molybdenum disulfideshould be present in the range of from about 2 parts by weight to about10 parts by weight per 100 parts by weight of the total absorptioncomposition.

In preparing the absorption composition, if the method of agglomerationof the mixture of the components is extrusion, as opposed to alternativemethods of agglomeration, a suitable acid can be used to prepare anextrudable paste. Any suitable acid can be used for forming anextrudable paste. Such suitable acids can be selected from the groupconsisting of nitric acid, acetic acid, sulfuric acid, hydrochloricacid, formic acid and mixtures of two or more thereof. Additionally,dilute solutions or aqueous solutions of such suitable acids can be usedin the preparation of the novel composition. Generally, it is preferredto use an aqueous solution of a suitable acid in the preparation of thecomposition with the concentration of the acid compound generally beingin the range of from about 1 weight percent to about 15 weight percent.Preferably, the concentration range will be from about 1 weight percentto about 5 weight percent. When referring herein to the weight percentconcentration of an acid compound in an aqueous solution of suchcompound, the term shall be defined as being the ratio of the weight ofsuch suitable acid compound to the weight of the total solutionmultiplied by a factor of 100.

While the preferred method for agglomerating the absorbent components isthe use of extrusion techniques, any suitable method of agglomerationcan be utilized to enlarge the size of the absorption material particlesand to form them into relatively permanent masses having a certaindesirable form such as spheroids, pills or tablets, cylinders, irregularextrusions or merely loosely bound aggregates or clusters. Examples ofsuch methods of agglomeration include, but are not limited to, molding,tableting, pressing, pelletizing, extruding, and tumbling. Whenutilizing extrusion methods for agglomeration, any suitable method andextrusion equipment can be used. It is preferred to use either asingle-screw extruder or a double-screw extruder which uses a screw oraugur to convey a force for passing the extrusion material through adie, plate to produce desirable shapes or extrusion profiles.

It is theorized that the presence of effective quantities of molybdenumdisulfide in the extrudable paste provides for lubricity of the pasteand lowers the coefficient of friction of the paste. Because of thisincreased lubricity and lowered coefficient of friction, the die wearcaused by the shear forces created by the passing of the extrusion pastethrough the holes of the extruder die plate is materially decreased. Itis desirable to provide an effective concentration of the molybdenumdisulfide in the novel absorption mixture such that extrusion die wearis reduced by upwardly to about 50 percent of the die wear that wouldnormally occur with the molybdenum disulfide not being present. Mostpreferably, extruder die wear will be reduced by at least 10 percent ofthe die wear that would normally occur with the molybdenum disulfide notbeing present. The die wear is determined by comparing the weight lossof an extruder die which occurs from extruding the prior art absorbentcompositions to the die wear loss which results from extruding the novelcomposition as described herein. The percent weight loss of die wear asused herein is defined by the ratio of the difference in weight lossbetween that caused by the prior art compositions and that caused by thenovel composition to the weight loss caused by the prior art compositionmultiplied by a factor of 100.

Once these absorbent components are properly mixed and agglomerated, themixture can advantageously undergo a drying step for removing certainquantities of water. The drying of the agglomerate can be conducted atany suitable temperature for removing excess quantities of water, butpreferably, the drying temperature will range from about 150° F. toabout 550° F. More preferably, however, the drying temperature shallrange from about 190° F. to about 480° F. Generally, the time period forsuch drying shall range from about 0.5 hour to about 4 hours and, morepreferably, the drying time shall range from about 1 hour to about 3hours. While the method and apparatus used for performing the optionaldrying step is not a critical aspect of this invention, many of thesuitable methods and apparatuses for drying the agglomerate aredescribed at length in Perry's Chemical Engineers' Handbook, pages 20-3through 20-75 (6th edition, 1984).

The wet agglomerate or the optionally dried agglomerate is then calcinedin the presence of an oxygen-containing fluid at a temperature suitablefor achieving the desired degree of calcination. For example, generallythe temperature shall range from about 700° F. to about 1,400° F. Morepreferably, the calcination temperature shall range from about 900° F.to about 1,300° F. The calcination step can be conducted for a period oftime suitable for achieving the desired degree of calcination, butgenerally, the time for calcination shall range from about 0.5 hour toabout 4 hours. Most preferably, the calcination time shall range fromabout 1hour to about 3 hours to produce a calcined absorbingcomposition.

In a preferred embodiment of the invention, a method of reducing sulfurslippage in an absorption process for removal of hydrogen sulfide from afluid stream having a contaminating concentration of hydrogen sulfide isprovided. The first step of this preferred embodiment includes adding byany suitable means the compound molybdenum disulfide to a contactmaterial comprising zinc oxide and silica to thereby produce anabsorbent suitable for use in said absorption process. The resultantabsorbent material is thereafter contacted with a fluid stream having acontaminating concentration of hydrogen sulfide under conditionssuitable for removing at least a portion of the contaminatingconcentration of hydrogen sulfide.

The process according to this invention can suitably process any type offluid streams containing contaminating concentrations of sulfurcompounds. Such sulfur compounds can include, for example, hydrogensulfide, carbonyl sulfide, carbon dioxide, carbon disulfide, andmercaptans. Any suitable fluid containing contaminating concentrationsof sulfur compounds can be processed in this invention. Suitable fluidscan include, for example, natural gas, synthesis gas, hydrocarbons, andtail gas from Claus reaction processes. It is preferred that ahydrocarbon fluid stream containing a concentration of hydrogen sulfidebe utilized in this invention. Generally, the concentration of thehydrogen sulfide in such a fluid stream will range upwardly to about60,000 parts per million by volume (ppmv). The term "parts per millionby volume" as used herein is defined as being 1 part by volume per 1million parts by volume of the reference fluid stream. Preferably, theconcentration of the hydrogen sulfide will range from 5,000 ppmv to40,000 ppmv and, most preferably, the concentration of the hydrogensulfide will range from 5,000 ppmv to 20,000 ppmv.

The sulfur contaminated fluid stream can be contacted by any suitablecontacting means with the absorbent resulting from the addition ofmolybdenum disulfide under conditions that are suitable for removing atleast a portion of the contaminating concentration of sulfur compoundsin the fluid stream. The operating conditions under which the contactingstep is conducted can be any suitable temperature, pressure or spacevelocity which will provide the desired sulfur removal. The operatingtemperature or contact temperature will generally be in the range offrom about 300° F. to about 1,100° F. and will more preferably be in therange of from about 400° F. to about 840° F. Such suitable operatingpressure shall range from about atmospheric to about 2,000 psia.

Any suitable space velocity for the sulfur compound containing fluidstream in the presence of the absorption composition of the presentinvention can be utilized. The space velocity is expressed as volumes offluid at standard temperature and pressure per volume of absorbingcomposition per hour will generally be in the range of from about 10 toabout 10,000 and will more preferably be in the range of from 250 to2,500.

As an additional optional step in the method for reducing sulfurslippage is that of calcining the absorbent, which is produced by addingmolybdenum disulfide to the contact material comprising zinc oxide andsilica, prior to the contacting step. The calcination of the absorbentcomposition is preferably conducted in the presence of anoxygen-containing gas such as, for example, air, at a temperature in therange of from about 700° F. to about 1,400° F. for a period of time inthe range of from 0.5 hour to about 4 hours.

The amount of molybdenum disulfide which is added to the contactmaterial comprising the zinc oxide and silica can range upwardly toabout 25 weight percent or, in the alternative, from at least a portionto about 25 weight percent; and, preferably, the amount of molybdenumdisulfide added will range from about 1 to about 15 weight percent. Mostpreferably, the amount of molybdenum disulfide added will range fromabout 2 to about 10 weight percent. The amount of the silica componentof the contact material comprising zinc oxide and silica can range fromeffective quantitites up to about 90 weight percent, preferably fromabout 30 to about 90 weight percent, and, most preferably from about 35to about 65 weight percent.

In another embodiment of the invention, a method is provided forreducing sulfur slippage in a process for absorbing hydrogen sulfidefrom a hydrogen sulfide contaminated fluid stream. This method ofreducing sulfur slippage is performed by contacting the fluid streamcontaining a contaminating concentration of hydrogen sulfide by anysuitable contacting means with a contact material comprising a mixtureof zinc oxide, silica, and molybdenum disulfide, which bas beenpreviously calcined, to produce an efficient stream having a reducedconcentration of said contaminating concentration of hydrogen sulfide.

The resultant effluent stream produced by the method described hereinwill generally have a reduced concentration of contaminating hydrogensulfide and of sulfur dioxide that passes through the absorptionmaterial unabsorbed. While some of the sulfur dioxide present in theeffluent stream can be sulfur dioxide that was present in the fluidstream being contacted with the absorption composition, much of thesulfur dioxide present in the effluent stream can be the result ofsulfur slippage. The term "sulfur slippage" as used herein is defined asthat amount of hydrogen sulfide, which is present in the fluid streambeing contacted with the absorption composition, that is converted intosulfur dioxide by the result of a reaction with active ingredientscontained within the absorption composition and that passes unabsorbedalong with the effluent stream from the contacting means. It is mostdesirable to have the amount of sulfur slippage minimized whilesimultaneously maximizing the amount of sulfur absorption upon theabsorbent material. The novel composition and method described hereinprovides the beneficial result of minimizing the amount of sulfurslippage. Generally, sulfur slippage will be less than 1,000 ppmv;however, it is most preferable to have a sulfur slippage of less than500 ppmv and, most preferably, the sulfur slippage should be less than100 ppmv.

To provide further improvements in the method for reducing sulfurslippage in a process for absorbing hydrogen sulfide, or for removal ofhydrogen sulfide from a fluid stream having a contaminatingconcentration of hydrogen sulfide, hydrogen can be provided or added tothe fluid stream containing such contaminating concentration of hydrogensulfide prior to or during the contacting of the fluid stream with thecontact material, which has been previously calcined, comprising amixture of zinc oxide, silica, and molybdenum disulfide. By adding orproviding hydrogen to the fluid stream to be contacted with theabsorbent material, significant and unexpected reductions in the amountof sulfur slippage are achieved. It is theorized that certain activecompounds within the contact material react with a certain quantity ofthe hydrogen sulfide in the hydrogen sulfide contaminated fluid streamto form sulfur dioxide. The sulfur dioxide formed within the fluidstream then passes from the contacting means. It is believed that apresence of hydrogen in the fluid stream can be effective for thereduction of at least a portion of the sulfur dioxide formed orcontained in the fluid stream to hydrogen sulfide. Any concentration ofhydrogen in the fluid stream that is effective in reducing sulfurslippage can be utilized in this method. Preferably, the amount ofhydrogen to be added to the fluid stream can range from about 0.1 toabout 1.9 volume percent of the fluid stream.

The following examples are presented in further illustration of theinvention.

EXAMPLE I

The following example illustrates the benefits that are derived frommixing molybdenum disulfide with the absorption components during themanufacture of the absorbent composition. Such benefits include, forexample, improved lubricating properties of the mixture with thecorresponding reduction in the coefficient of friction and the reductionin extruder die wear during the production of the absorbent compositionagglomerate.

A number of extrusion aides and lubricants were evaluated to determinewhether they could substantially reduce equipment wear during productionof various absorption compositions. The evaluation was done by extrudingequal quantities of material through soft metal dies of copper andaluminum in a 1-inch laboratory Bonnot extruder. After the extrusion,the weight loss from the dies was measured with the effectiveness of theadditives being determined by comparing the weight loss from theextrusion dies caused by the various comparative compositions. Theresulting data is reported in Table I.

Composition A is a mixture of zinc oxide and alumina with the amount ofzinc oxide representing half the weight of the composition and theamount of alumina representing the remaining half of the weight of thecomposition. Composition B is a mixture of 50 weight percent zinc oxide,40 weight percent silica, and 10 weight percent alumina. The absorbentcompositions were prepared by mixing the components with an acetic acidsolution to form an extrudable paste and thereafter extruding the pastethrough the dies of a 1-inch laboratory Bonnot extruder. As shown inTable I, no lubricant was mixed with composition A; and, for comparison,composition B bad no lubricant mixed therein. Further provided in TableI, are compositions B1, B2, B3, B4 and B5 which are compositions ofwhich the indicated lubricant is mixed with the composition B prior tothe extrusion of the extrudable paste through the indicated dies. Theweight loss resulting from extruding a fixed quantity of the indicatedcomposition for each of the metal dies is presented in Table I. Asindicated, the extrusion of composition A caused insignificant weightloss of the metal dies. However, composition B and the associatedcompositions all showed significant die wear which resulted from theextrusion of the compositions. The experimental lubricants providedvaried results with graphite having very little effect upon die weightloss and with the lubricants stearic acid and STP showing increases inthe amount of die weight loss. Molybdenum disulfide, however, was theonly lubricant which indicated substantial reductions in the amount ofdie wear with such reduction being as much as 50% when compared withcomposition B which bad no lubricant.

The data presented in Table I suggest that molybdenum disulfide, whenused as a lubricant, can significantly reduce the die wear caused by theabrasive nature of the silica contained within composition B.

                  TABLE I                                                         ______________________________________                                        Die Plate Wear During Extrusion (1)                                           Ab-               Lubricant                                                   sor-              Loading   Weight Loss (gm) from die                         bent Lubricant    (%)       Copper (2)                                                                            Aluminum (3)                              ______________________________________                                        A    None         0         0.00    0.00                                                        0         0.00    0.00                                      B    None         0         0.26    0.09                                      B1   Graphite     1         0.24    0.14                                                        1         0.24    0.12                                                        1         --      0.11                                      B2   MoS2         5         0.15    --                                                          10        0.15    0.07                                                        10        --      0.04                                      B3   Stearic Acid 1         0.40    --                                                          2         0.36    --                                        B4   STP          1         0.33    --                                        B5   Aquabind 5580 (4)                                                                          1         --      0.18                                                        1         --      0.09                                      ______________________________________                                         Notes:                                                                        (1) Each extrusion consisted of 1100 g of solids through the 1" laborator     Bonnot single screw extruder. The total extrusion time depended on the        material, but was typically between 20 and 30 minutes.                        (2) The copper die used was a 3/8" thick copper die with 4 holes (1/8"        diameter) in a circular pattern.                                              (3) The aluminum dies were 1/4 " thick grade T651 6061 T6 aluminum with       four 1/8" diameter holes.                                                     (4) Aquabind 5580 from Shamrock Technologies is an extrusion aide and         lubricant. It is a blend of a cellulose and a wax.                       

EXAMPLE II

This example illustrates the sue of the novel absorbent compositionwhich utilizes a molybdenum promoter which source was from themolybdenum disulfide utilized as a lubricant as described in Example II.This example not only shows that the molybdenum disulfide can be used asa lubricant in the manufacture of the novel composition, but it can alsobe used as a suitable promoter for improving sulfur absorption andsulfur slippage in the absorption process. This example furtherillustrates the benefits which are achievable by adding a smallconcentration of hydrogen to an absorption zone feed fluid containing aconcentration of hydrogen sulfide.

Illustrated in FIG. 1 and FIG. 2 are the results of experimental testingof absorbent compositions which contain a concentration of molybdenum.Further shown in FIG. 1 and FIG. 2 are the effects of utilizing hydrogenin the process feed fluid. The amount of hydrogen added to the processfeed was about one volume percent of the fluid stream.

In FIG. 1, the process and physical property data of the absorbingcomposition A, which was described in Example I but additionally havinga six (6) weight percent molybdenum promoter metal, is presented in theform of graphs with the number of regeneration cycles being illustratedon the x-axis and the pertinent process and physical property data beingrepresented on the y-axis. FIG. 1 illustrates the measured properties ofthe comparative absorbent composition A as described in Example I butadditionally having a promoter metal. As shown, the sulfur loadingcapacity ranged from approximately 14 weight percent sulfur with adecreasing ability to absorb sulfur as the number of regenerations ofthe absorbent increased. Additionally, there seems to be little benefitto the sulfur loading capacity of the composition from adding hydrogento the feed fluid stream. As for the sulfur slippage, at 10 minuteswithin a cycle, the amount of sulfur slippage is in the range of fromabout 1,000 ppmv to about 800 ppmv. The presence of hydrogen in theprocess fluid stream early in the cycle has little affect upon thesulfur slippage by only reducing it about 10% to 20%. However, thesulfur slippage at the end of the run ranges from about 400 ppmv toabout 300 ppmv, and when hydrogen is present in the feed fluid stream,the amount of sulfur slippage is reduced by as much as 90% to about 36ppmv. These data illustrate that composition A, having a concentrationof molybdenum, has both the desirable property of high sulfur loadingcapacity and the ability to absorb reduced sulfur compounds from processfluid streams with a minimum amount of sulfur slippage. Furthermore, thedata illustrated in FIG. 1 shows the benefit from adding a smallconcentration of hydrogen to a process fluid stream undergoing anabsorption step.

In FIG. 2 the process and physical property data of the absorbingcomposition B, which was described in Example I but additionally havinga six (6) weight percent molybdenum metal promoter, is presented in theform of graphs with the number of regeneration cycles being illustratedon the x-axis and the pertinent process and physical property data beingrepresented on the y-axis. As is shown in FIG. 2, the sulfur loadingcapacity ranged from approximately 17.5 weight percent with a slightdecrease in its ability to absorb sulfur as the number of regenerationsincreased. Additionally, there appears to be little benefit to thesulfur loading capacity of the composition from adding hydrogen to thefeed fluid stream. As for the sulfur slippage, at 10 minutes within acycle, the amount of sulfur slippage ranges from about 500 ppmv to about350 ppmv. The presence of hydrogen in the process fluid stream resultsin significantly reducing the amount of sulfur slippage by as much asabout 500 percent from about 125 ppmv to about 25 ppmv at end-of-runconditions and by as much as about 400 percent from about 400 ppmv toabout 100 ppmv at 10 minutes into a cycle.

The data presented in FIG. 1 and FIG. 2 show the process improvementsthat are achievable by utilizing the novel aspects of the inventiondescribed herein. The composition used in generating the data presentedin FIG. 2 shows superior and unexpected improvements in the absorptionprocess. First, the sulfur loading capacity of composition B with six(6) percent molybdenum promoter is significantly greater than that ofcomposition A with six (6) percent molybdenum. For instance, as canclearly be seen from the figures, the sulfur loading capacity of thecomposition of FIG. 1 is in the range of from about 14 to about 10weight percent; on the other hand, the sulfur loading capacity of thecomposition of FIG. 2 is significantly greater than that of FIG. 1 withit being in the range of from about 18 to about 17 weight percent.Second, the sulfur slippage for composition B with six (6) percentmolybdenum promoter is significantly less than that for composition Awith six (6) percent molybdenum. Sulfur slippage at 10 minutes into acycle for the composition of FIG. 1 is in the range of from about 1,000ppmv to about 800 ppmv whereas the sulfur slippage at 10 minutes into acycle for the composition of FIG. 2 is in the range of from about 525ppmv to about 325 ppmv. And, for end-of-run conditions, sulfur slippagefor the composition of FIG. 1 is in the range of from about 575 ppmv andabout 300 ppmv whereas the sulfur slippage for the composition of FIG. 2is in the range of from about 250 ppmv to about 125 ppmv.

When a thorough comparison is made between the data as presented in FIG.1 and FIG. 2, it is clear that superior results are obtainable by usingthe composition of FIG. 2 in an absorption process. By utilizing thecomposition of FIG. 2, improvements both in sulfur loading capacity andsulfur slippage are obtained giving a sulfur loading capacity that issignificantly higher than that of the composition of FIG. 1 and giving asulfur slippage significantly lower than that of the composition ofFIG. 1. Additionally, by adding one (1) volume percent hydrogen to theprocess feed fluid, sulfur slippage can be reduced by as much as about500 percent under sulfur slippage that can occur when no hydrogen isadded to a process feed fluid.

The inventive composition as described herein provides for an improvedabsorption composition which has a high sulfur absorption capacity and,when utilized in an absorption process, provides minimum sulfurslippage. Furthermore, the data presented herein illustrate that theinventive composition can undergo many regeneration cycles and stillmaintain the desirable physical properties of high sulfur loadingcapacity and the provision of low sulfur slippage. Additionally, thenovel absorbent manufacturing method described herein can significantlyreduce the amount of extrusion equipment wear in the manufacture of thenovel composition. Moreover, when the inventive composition is used inan absorption process and small quantities of hydrogen are added to theprocess feed fluid stream, further reduction in sulfur slippage isobserved thereby improving the sulfur absorption process.

Reasonable variations and modifications are possible within the scope ofthis disclosure without departing from the scope and spirit thereof.

That which is claimed is:
 1. An absorbent composition consistingessentially of:zinc oxide; silica; and at least some molybdenumdisulfide up to about 25 parts by weight molybdenum disulfide per 100parts by weight of the sum weight of zinc oxide, silica, and molybdenumdisulfide.
 2. An absorbent composition as recited in claim 1 whereinsaid silica is present in the range of from about 30 to about 90 partsby weight per 100 parts by weight of the sum weight of zinc oxide,silica, and molybdenum disulfide.
 3. An absorbent composition as recitedin claim 2 wherein said molybdenum disulfide is present in aconcentration range suitable for imparting said lubricating propertiesto said absorbent composition such that when said absorbent compositionundergoes an extrusion through extrusion dies, the die wear is reducedby upwardly to about 50 percent.
 4. An absorbent composition as recitedin claim 3 wherein said molybdenum disulfide is present in aconcentration range suitable for promoting the reduction of at least aportion of sulfur dioxide contained in a fluid stream to hydrogensulfide when skied fluid stream contains a concentration of sulfurcompounds and is contacted with said absorbent composition in thepresence of reducing quantities of hydrogen.
 5. An absorbent compositionas recited in claim 4 wherein said molybdenum disulfide is present inthe range of from about 2 to about 10 parts by weight per 100 parts byweight of the sum weight of zinc oxide, silica, and molybdenumdisulfide.
 6. An absorbent composition as recited in claim 5 whereinsaid absorbent composition has been calcined in the presence of anoxygen-containing gas at a temperature in the range of from about 700°F. to about 1,400° F. for a period of time of from about 0.5 hour toabout 4 hours.
 7. A method of producing a zinc oxide based absorbentcontaining a regeneration aiding amount of molybdenum disulfidecomprising the steps of:mixing molybdenum disulfide with zinc oxide andsilica in an amount to provide a mixture comprising a regenerationaiding amount of molybdenum disulfide said amount ranging from at leasta portion to about 25 parts by weight molybdenum disulfide per hundredparts by weight of the sum weight of zinc oxide, silica and molybdenumdisulfide thereby forming a mixture also having extrusion dielubricating properties; adding to said mixture a dilute acid suitablefor forming an extrudable paste from said mixture; and extruding saidextrudable paste through an extrusion die to produce an extrudate ofsaid zinc oxide based absorbent containing a regeneration aiding amountof molybdenum.
 8. A method as recited in claim 7 wherein said mixturecontains molybdenum disulfide in an amount from about 2 to about 10parts by weight molybdenum disulfide per 100 parts by weight of the sumweight of zinc oxide, silica and molybdenum disulfide.
 9. A compositionprepared by the method of claim
 8. 10. A method as recited in claim 8wherein said silica is present in said mixture in the range of fromabout 30 to 90 parts by weight per 100 parts by weight of the sum weightof zinc oxide, silica, and molybdenum disulfide.
 11. A compositionprepared by the method of claim
 10. 12. A method as recited in claim 10wherein said dilute acid is an aqueous solution of acid compoundsselected from the group consisting of nitric acid, acetic acid, sulfuricacid, hydrochloric acid, formic acid and mixtures of two or morethereof.
 13. A composition prepared by the method of claim
 12. 14. Acomposition prepared by the method of claim
 7. 15. A method of preparingan absorbent having an improved ability to minimize sulfur slippage in aprocess for absorbing hydrogen sulfide from a fluid stream whencontacted with said fluid stream in the presence of a small amount ofhydrogen, comprising:mixing zinc oxide, silica, and at least somemolybdenum disulfide up to about 25 parts by weight molybdenum disulfideper 100 parts by weight of the sum weight of zinc oxide, silica, andmolybdenum disulfide to form a mixture; adding to said mixture a diluteacid suitable for forming an extrudable paste from said mixture;extruding said extrudable paste to produce an extrudate; and calciningsaid extrudate.
 16. A method as recited in claim 15 wherein the amountof silica used in said mixing step shall range from about 30 to about 90parts by weight per 100 parts by weight of the sum weight of zinc oxide,silica, and molybdenum disulfide and wherein the amount of molybdenumdisulfide used in said mixing step shall range from about 1 to about 15parts by weight per 100 parts by weight of the sum weight of zinc oxide,silica, and molybdenum disulfide.
 17. A method as recited in claim 16wherein said dilute acid is an aqueous solution of acid compoundsselected from the group consisting of nitric acid, acetic acid, sulfuricacid, hydrochloric acid, formic acid and mixtures of two or morethereof.